Instant-on filament heating circuits



Aug. 29, 1967 1 1 BUSSE 3,339,105

INSTANT-ON FILAMENT HEATING CIRCUITS Filed Sept, '7, 1965 John J. BusseAffy.

positive temperature coefficients United States Patent O 3,339,105INSTANT-ON FILAMENT HEATING CIRCUITS John J. Busse, River Grove, Ill.,assigner to Admiral Corporation, Chicago, Ill., a corporation ofDelaware Filed Sept. 7, 1965, Ser. No. 485,501 6 Claims. (Cl. 315-101)This invention concerns instant-on circuits for electronic apparatus,especially television receivers and the like.

Recently there has been great impetus in the area of providing vacuumtube operated television receivers which no longer require relativelylong warm-up times-usually on the order of one minute. It has beenproven desirable, from a customer point of view, to manufacturetelevision receivers which are capable of giving substantiallyinstantaneous sound and picture.

Obviously, with vacuum tubes and other temperature dependent devices,there must be provision for maintaining these devices at or nearoperating temperature for instant operation. A plus factor in theinstant-on development is that, if properly designed, vacuum tubesactually experience longer service life since damaging current surgesdue to cold start-up are eliminated. It is well known that most vacuumtubes employ tungsten filaments which have of resistance. Thus, as thefilament resistance also increases. Consequently, when the filament iscold its resistance is low, and the initial current is much higher thannormal operating current.

It is not feasible to maintain the vacuum tube heaters at full operatingtemperature for at least two reasons. The first is that the cathodesunduly age when operated at near normal electron emitting temperaturesunless operating potentials on the other tube elements are maintained.This phenomenon has been colloquially called sleeping sickness.Experimentation Ihas shown that the cathode may be maintained at lessthan full operating temperatures without presenting any serious problemsin this respect. It has been determined that the filaments may beoperated at one-half power consistent with substantially instant-onoperation and good aging characteristics of the cathode. A second reasonis one of simple economics in that it is desirable to minimize the powerloss in the receiver during its off condition. Consequently, among thenumerous proposals is a circuit type utilizing a diode in series withthe heater or filament string for conveniently limiting the currenttherethrough durng off periods.

The diode offers the advantage of current limiting without the powerloss attendant upon resistive limiting, or without requiring a tappeddown transformer or other voltage reducing device. The advantagesaccruing as a result of the use of a diode are well known and notclaimed as any part of this invention.

Some circuits utilize a separate diode with a switching arrangement forplacing the separate diode in the heater string in the off position ofthe apparatus, whereas others provide for switching the diode which isalready present in the receiver power supply into the heater circuitduring off time.

The circuit of the invention utilizes a separate diode, but does nothave any complicated switching. Further, the diode used need not havethe current rating of the power supply diode. l

There is an advantage in simplifying the switching in the receiver apartfrom that of eliminating stacked switches and their tendency tomechanical problems. In fact, most on-off television switches arealready encumbered with volume controls or the like. Additionally, incolor sets, the on-off switch may already have an additional stackedswitch thereon for providing so-called automatic degaussing. In somemonochrome sets a switch may temperature increases,

ICC

be coupled to the on-off switch for preventing the damaging bright spotin the center of the picture tube which may occur after the set isturned off. Thus there often is insufficient room to place furtherswitching functions on the on-off switch and wholly separate switchesmay not be practical or feasible economic-ally.

In accordance with the teachings of the invention, a simple diode isconnected in parallel with the on-off switch of the television receiver,but in polarity'opposition to the diode in the DC voltage supplycircuit. When the switch is in the ON position, the diode is effectivelyshort-circuited, and circuit operation is normal. When the switch is inthe OFF position, the heater string and the DC power supply are bothconnected to the source of alternating current potential through thediode. The heater string thus receives rectified AC for operation atlower than normal temperatures, whereas the DC supply circuit isdisabled since the additional diode is oppositely poled to the rectifierdiode.

Accordingly, the principal object of this invention is to provide animproved instant-on circuit for use with electronic apparatus employingvacuum tubes.

Another object of this invention is to provide an instanton circuitwhich may be readily incorporated in existing television receivers ofthe -low B| type (those incorporating half wave rectification in thepower supply).

A further object of this invention is to provide an instant-on circuitwhich does not require any ladditional mechanical parts.

Further objects of this invention will be readily apparent upon readingthe following specification in conjunction with the drawing whichdiscloses in partial block, partial schematic form the essential circuitelements and configuration.

The drawing shows a block 10 labeled TELEVISION RECEIVER which should beunderstood to incorporate all of the necessary conventional circuitryfor receiving a television signal, detecting the signal, and reproducingboth the audio and visual information contained therein on suitablereproducing means. Since the televisori art is quite well developed andsince the present invention does not require the exposition ofparticular circuit functions, it is not believed necessary to discloseindividual circuitry therein.

A source of alternatingcurrent 11 is shown having a pair of leadsextending into block 10. One lead is connected to a common source ofground potential and the other to a switch 12 having ON and OFFterminals. The ON terminal of switch 12 is connected to a series ofheater elements 24, 24A 24N, to ground. (The dashed lines joining tubes20A and 20N indicate that any number of tubes may be incorporated.) Thisterminal is also connected to the anode 14 of a rectifier 13. Thecathode 15 of rectifier 13- is connected to a conventional filtercircuit comprising a pair of electro-lytic filter capacitors 16 and 18bridged by a filter choke 17. The junction of filter choke 17 andcapacitor 18 is the B+ point for the television receiver.

The television receiver includes a plurality of vacuum tubes 20, 20A 20Nfor performing various well known operations on the received televisionsignal. These vacuum tubes all include heater elements and signalprocessing elements. Vacuum tube 20, for example, comprises an anode 21,a cathode 22, and a control element 23. Heater 2.4 has already beendiscussed and a simple load resistor 25 is connected between anode 21and the B+ point. Similarly, vacuum tube 20A has an anode 21A, a cathode22A, a control element 23A, a heater 24A, and a load impedance 25A. Itshould be obvious that many more vacuum tubes are utilized in modern daytelevision receivers to perform the basic functions alluded to brieflyabove, but, for purposes of simplicity, only three such tubes areillustrated. It should be further understood that while the illustratedheater elements are shown connected in series they may be connected inany desired arrangements, as long as only one source of supply voltageis required.

An addit-ional diode 30 is connected to switch 12 such that switch 12short circuits diode 30 when in the ON position. Diode 30 has an anode31 and a cathode 32 and is arranged to have a polarity with respect tothe source that is opposite to diode 13 in the DC voltage supply.

During normal operation, that is with switch 12 in the ON position,alternating current from source 11 passes through series connectedheater elements 24, 24A 24N in a complete circuit which bypasses diode30. The heater element circuit is designed such that when the televisionreceiver is connected to a proper source of alternating currentpotential, predetermined currents fiow therethrough, which causespredetermined operating temperatures for their associated cathodes 2222N. Simultaneously, the alternating current from source 11 is rectifiedby diode 13 and filtered by capacitors 16 and 18 and choke 17 to providea source of direct current for the signal processing elements of thevarious vacuum tubes in the receiver. Thus,lthe circuit will be seen tooperate in a normal manner when switch 12 is in the ON position.

However, when switch 12 is placed in the OFF position, diode 30 iselectrically in series with source 11 and the receiver. Since the heaterelement circuit and the DC supply circuit are effectively connected inparallel, diode 30 is a common series element in both of these circuits.Now alternating cur-rent from source 11 is rectified by diode 30 and theheater elements receive substantially half` of the current that theynormally receive when switch 12 is in the ON position. Accordingly,their associated cathodes achieve something less than normal operatingtemperatures.

Since the polarity of diode 30 is opposite to that of diode 13, thealternating current is effectively blocked from the television receiversignal processing elements. Thus, during the off periods, the televisionreceiver heater elements are operated at less `than normal operatingtemperatures, and the receiver B+ circuit is effectively disabled.

This operation has been accomplished by the simple addition of arelatively low power diode connected across the on-off switch. Thecurrent rating of the diode is naturally based upon the normal currentdrawn by the heater circuit and will be approximately one-half normal.The voltage breakdown rating need only be sufficient for the linevoltage involved. Hence, a relatively uncritical, inexpensive diode maybe used. l-t will be noted also that many existing electronic apparatusmay be readily connected to instant-on operation by the simple expedientof adding a diode acr-oss the on-off switch terminals.

What has been described is a simple, efficient circuit for providinginstant-on operation in vacuum tube apparatus. While a specificembodiment of the invention has been disclosed for descriptive purposes,it will be appreciated that the scope of the invention is limited onlyas defined in the claims.

The embodiments lof the invention in which an exclusive property orprivilege is claimed are defined as follows:

y1. In a television receiver; a plurality of vacuum tubes having heaterelements connected in an electrical circuit normally operable from asource of alternating current; a direct current circuit including afirst rectifier; an alternating current source; an on-off switchconnected between said alternating current source and both said directcurrent circuit and said heater element circuit; and a second rectifierparalleling said switch, said second rectifier being poled in oppositionto said first rectifier whereby when said switch is closed said heaterelement circuit and said direct current circuit are connected directlyto said alternating current source and when said switch is open saidheater element circuit is supplied rectified current and said directcurrent circuit is rendered ineffective.

2. In electronic apparatus, a plurality of vacuum tubes having a heatercircuit designed for operation on alternating current; a direct currentsupply circuit for said vacuum tubes, both said circuits being connectedin parallel and forming a power load circuit; an alternating currentsource; a single pole-two position switch connected between saidalternating current source and said power load circuit; said directcurrent supply circuit including a first rectifier passing one polarityof electrical current; and a second rectifier connected in parallel withsaid switch and poled to pass the opposite polarity of electricalcurrent whereby when said switch is one position said power load circuitreceives normal power from said alternating current source and when saidswitch is in the other position said heater circuit is energized fromsaid alternating current source through said second rectifier and saiddirect current supply circuit draws substantially no power from saidalternating current source.

3. A power supply for an electronic tube system having a plurality oftubes with heaters being connected to form a heater circuit; a pair ofterminals adapted to be connected to a source of alternating current; afilter circuit including a first rectifier; an on-off switch connectedto both said filter circuit and said heater circuit for completing abi-directional current path including said circuits and said terminalswhen in ythe ON position; a second rectifier paralleling said on-offswitch and poled opposite to said first rectifier whereby when saidon-off switch is in the OFF position said heater circuit is in serieswith said second rectifier, and said first rectifier and said filtercircuit are rendered ineffective.

4. In combination with electronic apparatus including a vacuum tubehaving a heater element normally energizable from a source ofalternating current and other elements energizable from direct current;a source of alternating current potential; rectifying means passing onepolarity of current for deriving direct current from said source;switching means coupling said rectifying means and said heater elementto said source; and a standby circuit for maintaining said heaterelement operable at less than normal temperature and said other elementsat substantially zero potential, said circuit including furtherrectifying means connected across said switching means and passing theopposite polarity of current whereby said further rectifying means arerendered effective only when said switching means is in its opencondition.

5. An instant-on circuit for a television 4receiver including aplurality of vacuum tubes having heater elements designed for operationon AC and signal processing elements designed for operation on DC; asource of alternating current; an on-off switch; power supply meansncluding a first semi-conductor rectifier connected in circuit with saidsignal processing elements; circuit means connecting said on-off switchbetween said source and both said heater element circuit and said powersupply means whereby when said switch is in its ON position said heaterelement circuit and said power supply means are connected to said sourcefor normal operation; and a second low current semi-conductor rectifiercoupled across said on-off switch in opposite polarity to said firstrectifier whereby when said on-off switch is in the OFF position saidheater element is fed pulsating direct current for maintaining saidheater elements at less than normal temperature and said power supplymeans is effectively disabled.

6. An instant-on circuit for a television receiver including a pluralityof vacuum tubes having heater elements designed for operation on AC andsignal processing elements designed for operation on DC; a source ofalternating current; an on-off switch; halt wave power supply meansincluding at least one semi-conductor rectifier connected in circuitwith said signal processing elements for 5 developing a first magnitudeDC voltage therefor; circuit means connecting said on-Off switch betweensaid source and both said heater element circuit and said half wavepower supply means whereby when said switch is in its ON position saidheater element circuit and said half wave power supply mea-ns areconnected to said source for normal operation; and a low currentsemi-conductor rectifier coupled across said on-off switch in oppositepolarity to said one rectifier whereby when said on-oif switch is `inits OFF position said heater element is fed pulsating direct current formaintaining said heater elements at less than normal temperature andsaid half wave power supply means is elfectively disabled, said lowcurrent semi-conductor rectier having a reverse voltage rating slightlygreater than said first magnitude DC voltage.

References Cited UNITED STATES PATENTS 2,563,740 8/ 1951 Parker 328-2622,658,140 11/1953 Koch 328-270 2,931,946v 4/1960 Doncese et a1. 315-963,171,083 2/1965 Heifron 328-260 10 3,171,084 2/ 1965 Sziklai 328-270JOHN W. CALDWELL, Acting Primary Examiner. R. L. RICHARDSON, AssistantExaminer.

1. IN A TELEVISION RECEIVER; A PLURALITY OF VACUUM TUBES HAVING HEATERELEMENTS CONNECTED IN AN ELECTRICAL CIRCUIT NORMALLY OPERABLE FROM ASOURCE OF ALTERNATING CURRENT; A DIRECT CURRENT CIRCUIT INCLUDING AFIRST RECTIFIER; AN ALTERNATING CURRENT SOURCE AN ON-OFF SWITCHCONNECTED BETWEEN SAID ALTERNATING CURRENT SOURCE AND BOTH SAID DIRECTCURRENT CIRCUIT AND SAID HEATER ELEMENT CIRCUIT; AND A SECOND RECTIFIERPARALLING SAID SWITCH, SAID SECOND RECTIFIER BEING POLED IN OPPOSITIONTO SAID FIRST RECTIFIER WHEREBY WHEN SAID SWITCH IS CLOSED SAID HEATERELEMENT CIRCULAR AND SAID DIRECT CURRENT CIRCUIT ARE CONNECTED DIRECTLYTO SAID ALTERNATING CURRENT SOURCE AND WHEN SAID SWITCH IS OPEN SAIDHEATER ELEMENT CIRCUIT IS SUPPLIED RECTIFIED CURRENT AND SAID DIRECTCURRENT CIRCUIT IS RENDERED INEFFECTIVE.